[dm-devel] Using device-mapper with many targets

[Tom Parker]

Tom Parker wrote:
> With RAID 1 targets, I can get up to about 600 targets before the whole 
> thing seems to lock hard (dmsetup itself gets OOM'ed, and I can't get 
> back to the shell or to any other of the virtual terminals). While 
> scaling up to that point, I find that for every RAID 1 target, 
> device-mapper seems to eat ~.5MB of RAM. The targets themselves are 
> currently very small (1MB I think) as this was more a test in many 
> targets, rather than in large targets.

I've been trying to investigate this on my own, and ran into the issue 
that there's both a dm-raid1.c file in the 2.6.22 kernel, *and* in the 
device-mapper CVS. Additionally, the dm-raid1.c in the device-mapper CVS 
appears to be out of sync with current kernels. This does raise the 
issue of which one I should be investigating regarding the memory issues....

Any good reason why this is? Should I just be looking at the current 
kernel versions of that file?

Thanks,

Tom

P.S. If anyone knows any good tools for getting per-module memory usage 
(preferably with alloc/free tracing) out of the kernel, I'd love to know 
about them. I'm tempted at the moment to go with manual printk adding 
just because it's simple and it'll work.